On Dec. 29, the Centers for Disease Control (CDC) released the latest data on the spread of seasonal influenza in the United States. The data was through Dec. 20, nine days old. Media outlets have seized upon the report to declare that the U.S. is in the middle of a serious influenza epidemic. That is not true.
The data from Dec. 20 will not be updated until Jan. 2, according to the CDC. Media , however, have taken some of the Dec. 20 data and made claims that are not correct. CNN published a story titled “CDC: Flu at epidemic level; 15 children dead this season” on Dec. 31. The Sacramento Bee published one dated Dec. 30 titled “Flu season is officially at epidemic levels, CDC says.”
What sort of epidemic is the CDC talking about? The agency collects voluntary data on causes of death weekly through the 122 Cities Mortality Reporting System. One of the causes is “pneumonia and influenza” and 6.8 percent of all deaths for the week ending Dec. 20 were due to that cause. That rate reached the threshold for epidemic the CDC calculated for that week using historical data.
The American Lung Association states that one third of all pneumonia cases in the United States are due to a respiratory virus. In adults, influenza is the most common cause of viral pneumonia. Viral pneumonia is the most dangerous in those with preexisting lung problems such as asthma, COPD, as well as cardiac disease or pregnancy.
Other viruses that cause pneumonia include respiratory syncytial virus, rhinovirus, herpes simplex virus, severe acute respiratory syndrome (SARS) virus, and more.
How prevalent is influenza? One measure is the percentage of positive specimens from patients tested each week by the CDC and its partners. For the week, these laboratories conducted 21,858 tests. Just over 28 percent of the tests were positive for influenza. That percentage can vary by region. In the Rockies, the rate is over 35 percent while in New England it is just over 11 percent.
The rates for positive lab tests show that there are also other viruses in circulation that cause influenza-like illnesses (ILIs). MERS was in the news early in 2014 and it is caused by one of many corona viruses which may produce an ILI. Enteroviruses such as EV D68 also circulate and cause ILIs. It is also the time of year when infections by the respiratory syncytial virus peak and it, too, causes ILIs.
Several pieces of information in the CDC weekly report are important. The flu vaccine for this season is effective whether the patient receives the three virus or four virus formulation. All four of the influenza virus strains covered by the vaccine are in circulation and causing illness.
A fifth strain, the so-called “mutation”, is the most widely identified by laboratory testing. The influenza vaccine has one component that is distantly related and the CDC says that the vaccine may provide limited immunity. There will be no vaccine for this strain for this flu season.
Along with a vaccine to prevent the flu, there are also two anti-viral medications that will kill the flu virus. If taken within the first 48 hours after symptoms begin, Tamiflu or Relenza may decrease the length of the illness and lessen the severity of its symptoms. There is no vaccine or any anti-viral treatment for the thousands of other viruses that can cause an influenza-like illness.
The data does not show that there is an epidemic of influenza. It shows that influenza and the other viruses that cause respiratory infections are in wide circulation and causing more such illnesses than average. The flu season usually peaks in January or early February. It is still not too late to obtain a flu shot, which is effective against some of the influenza viruses causing illness at this time.